Thank you for your reply and recommendations

We are running swift on CentOS 6.5

getconf ARG_MAX returns
2621440

The small bash snippet you posted seems to be working on our machines too.

however the way we checked the limit is by xargs --show-limits which outputs:
POSIX smallest allowable upper limit on argument length (all systems): 4096

and as such we concluded the limit is 4096, also the rsync command itself stops suddenly at 4096 characters when checking the command with something like ps aux | grep rsync

The log looks something like this when failing with rsync:
account-replicator: Beginning replication run
Jan 21 04:12:55 srv-hostname account-replicator: Replication run OVER
Jan 21 04:12:55 srv-hostname account-replicator: Attempted to replicate 0 dbs in 0.00171 seconds (0.00000/s)
Jan 21 04:12:55 srv-hostname account-replicator: Removed 0 dbs
Jan 21 04:12:55 srv-hostname account-replicator: 0 successes, 0 failures
Jan 21 04:12:55 srv-hostname account-replicator: no_change:0 ts_repl:0 diff:0 rsync:0 diff_capped:0 hashmatch:0 empty:0
Jan 21 04:12:59 srv-hostname object-replicator: Killing long-running rsync: ['rsync', '--recursive', '--whole-file', '--human-readable', '--xattrs', '--itemize-changes', '--ignore-existing', '--timeout=30', '--contimeout=30', '--bwlimit=0'
, '/srv/osd/objects/2736/1c1', '/srv/osd/objects/2736/588', '/srv/osd/objects/2736/fa0', '/srv/osd/objects/2736/1c2', '/srv/osd/objects/2736/f78', '/srv/osd/objects/2736/574', '/srv/osd/objects/2736/46c', '/srv/osd/objects/2736/3db', '/sr
v/osd/objects/2736/604', '/srv/osd/objects/2736/ff0', '/srv/osd/objects/2736/542', '/srv/osd/objects/2736/a6e', '/srv/osd/objects/2736/36e', '/srv/osd/objects/2736/e50', '/srv/osd/objects/2736/771', '/srv/osd/objects/2736/8dd', '/srv/osd/
objects/2736/cba', '/srv/osd/objects/2736/d06', '/srv/osd/objects/2736/512', '/srv/osd/objects/2736/fd2', '/srv/osd/objects/2736/bb7', '/srv/osd/objects/2736/670', '/srv/osd/objects/2736/923', '/srv/osd/objects/2736/352', '/srv/osd/object
s/2736/ab7', '/srv/osd/objects/2736/2ca', '/srv/osd/objects/2736/809', '/srv/osd/objects/2736/1cc', '/srv/osd/objects/2736/d42', '/srv/osd/objects/2736/5b6', '/srv/osd/objects/2736/9b2', '/srv/osd/objects/2736/023', '/srv/osd/objects/2736
/cdb', '/srv/osd/objects/2736/01e', '/srv/osd/objects/2736/694', '/srv/osd/objects/2736/1b9', '/srv/osd/objects/2736/a15', '/srv/osd/objects/2736/bd4', '/srv/osd/objects/2736/af0', '/srv/osd/objects/2736/efe', '/srv/osd/objects/2736/c72',
 '/srv/osd/objects/2736/d3d', '/srv/osd/objects/2736/884', '/srv/osd/objects/2736/978', '/srv/osd/objects/2736/f2f', '/srv/osd/objects/2736/8ee', '/srv/osd/objects/2736/72f', '/srv/osd/objects/2736/f62', '/srv/osd/objects/2736/2af', '/srv
/osd/objects/2736/9a1', '/srv/osd/objects/2736/60c', '/srv/osd/objects/2736/273', '/srv/osd/objects/2736/cbd', '/srv/osd/objects/2736/8e3', '/srv/osd/objects/2736/69c', '/srv/osd/objects/2736/e5c', '/srv/osd/objects/2736/8c6', '/srv/osd/o
bjects/2736/bb6', '/srv/osd/objects/2736/e8f', '/srv/osd/objects/2736/37b', '/srv/osd/objects/2736/2c5', '/srv/osd/objects/2736/0c5', '/srv/osd/objects/2736/bd2', '/sr
Jan 21 04:13:01 srv-hostname container-replicator: Beginning replication run
Jan 21 04:13:02 srv-hostname container-replicator: Replication run OVER
Jan 21 04:13:02 srv-hostname container-replicator: Attempted to replicate 392 dbs in 0.92884 seconds (422.03307/s)
Jan 21 04:13:02 srv-hostname container-replicator: Removed 0 dbs
Jan 21 04:13:02 srv-hostname container-replicator: 0 successes, 0 failures

We tried increasing the rsync_timeout to 4 hours, but that doesn't help, as the destination path is missing because of the characters limit, we think.

The handoffs_first looks interesting and we are looking into it